In an oil and gas drilling process, the information about a current direction of a drill bit is critical to ensure drilling in the reservoir. Therefore, in addition to conventional drilling tool assembly, directional drilling also involves using position sensors to measure an attitude of a downhole drilling tool, providing information about an azimuth angle (an angle with the north direction in a horizontal plane) and an inclination angle (an angle with a vertical direction, also known as an inclination angle of the borehole) and a toolface angle (equivalent to a roll angle in navigation). An accurate measurement of the attitude of the downhole drilling tool not only ensures efficient drilling of an intended target, but also avoids the risk of collision with adjacent wellbore.
At present, attitude parameters of the drilling tool are generally measured by a Measurement While Drilling (MWD) system installed about 10 meters behind the drill bit. The MWD system integrates a three-axis accelerometer and a three-axis magnetometer, when an azimuth angle, an inclination angle and a toolface angle are measured, an operation of drilling must be stopped (that is, the drilling tool does not rotate), which is called a static measurement. Although accurate attitude parameters can be obtained with the MWD system, there are problems such as low time efficiency and high cost. In order to further improve a drilling efficiency, it is currently a hot research topic in the field of drilling tool attitude measurement for achieving continuous, dynamic and real-time measurement of the attitude parameters of the drilling tools.
In the research and development of a drilling tool attitude measurement module, it is necessary to build a testing device on the ground to simulate an attitude and a rotation state of the drilling tool in a well, and realize a calibration, testing and performance verification of instruments.
An existing calibration and testing device for the MWD system mainly includes a three-axis manual non-magnetic turntable and a three-axis electric non-magnetic turntable. A three-axis non-magnetic turntable and a three-axis inclinometer calibration table disclosed in patents CN202421522U and CN2015897611U both belong to manual non-magnetic turntables. When this type of turntable is used, three axial directions are all manually adjusted. According to a dial reading, when the turntable is turned to a set angle, a module to be tested is locked, and then the module is tested. This type of turntable can only be used for static calibration and testing. A three-axis non-magnetic calibration table disclosed in the patents CN103837161A and CN202017484U simply improves the mode of reading from a mechanical dial reading to a photoelectric encoder or micro camera automatic reading, and can only be used for manual static calibration and testing. Therefore, an angle adjustment of the existing manual three-axis non-magnetic turntable is manually operated, and data is read through a dial, which can only be used for a static test rather than a dynamic test at a certain rotation speed, and cannot be used for dynamic calibration test of an attitude measurement instrument.
Regarding the existing three-axis electric non-magnetic turntable, the patents CN204346451U and CN204329980U disclose technical solutions of an electric three-axis non-magnetic turntable, in which three axial directions are all electrically adjusted, but the main structure of a U-shaped support with a base is not able to operate stably under a condition of a large weight and a high rotation speed. At the same time, a toolface shaft is a hollow shaft tube, and both ends thereof are fixed by a taper sleeve nut, which is only suitable for a module having a regular round rod shape to be tested.
Therefore, in order to simulate a state of rotation of a drilling tool and realize a dynamic test of an attitude measurement module, it is necessary to develop a dynamic testing device capable of bearing large weight (above 30 kg), having a high rotation speed (maximum rotation speed up to 500 rpm) which is measurable and controllable, convenient for mounting and fixing a tested module and capable of rotating smoothly.